Magnetic random access memory (MRAM) devices are emerging as possible replacements for conventional RAM memory structures such as dynamic and static RAM structures. MRAM devices exhibit similar access speeds and greater immunity to radiation compared to conventional DRAM and SRAM structures, and advantageously do not require applied power to retain their logical state.
FIG. 1 illustrates a block diagram of a conventional MRAM device structure. The MRAM structure generally includes a “free” or storage layer 102, a reference layer 104, and a barrier junction 106 therebetween. The storage and reference layers 102 and 104 are formed from materials that possess a particular magnetic orientation, the relative orientations of which are either parallel, in which case the MRAM cell has a relatively low impedance between top and bottom electrodes 110a and 110b, or anti-parallel in which case the MRAM cell has a relatively high impedance between top and bottom electrodes 110a and 110b. 
The storage layer 102 will typically consist of a material that has a lower magnetic coercivity, and can therefore more easily be re-oriented, compared to the reference layer 104. Reading the state of the MRAM cell is performed by passing a predefined current between the top and bottom electrodes 110a and 110b, and monitoring the resulting voltage (or vice versa). Programming can be performed using one of two conventional techniques. One programming technique is to apply word and bit line currents along a particular direction to a particular MRAM memory cell at the word and bit line intersection, the current applied at a sufficient magnitude to induce a change in the magnetization of the MRAM device. However, this approach requires the generation of high current drive levels, resulting in high power dissipation levels and the requirement of large gate periphery transistors to handle the peak current conditions.
Thermally-assisted programming represents another MRAM programming technique. In this approach, a heating current is supplied across the MRAM's barrier layer, the resistance of which causes the storage layer to heat to a predefined temperature. The storage layer is preferably constructed from a material that exhibits a decreasing magnetic coercivity with increasing temperature, such that when the storage layer is sufficiently heated, lower magnitude writing currents can be used to re-orient the existing magnetic polarization of the storage layer.
Re-orientation with even lower magnitude writing currents can be achieved by using a storage layer combined with an anti-ferromagnetic layer. In such a structure the anti-ferromagnetic layer is pinning the existing magnetic polarization of the storage layer as long as the anti-ferromagnetic layer is kept below its blocking temperature. Since magnetic coercivity of the storage layer itself can be lower, writing currents can be lower, too. But re-orientation of the existing magnetic polarization of the storage layer will usually only work if the anti-ferromagnetic layer is heated up above its blocking temperature, therewith becoming inactive.
Unfortunately, materials having best physical attitudes for being used as anti-ferromagnetic layer and materials having best physical attitudes for being used as storage layer or reference layer do not necessarily show expected attitudes when in contact to each other. They may, for example, show unexpected low pinning forces.
What is therefore needed is an MRAM structure with an anti-ferromagnetic layer overcoming above-mentioned drawbacks.